Is this kitten still with his mother? It is ideal for them to stay with their mommy until about 10 weeks. You haven't given much detail on his background, but it is very very very hard to overfeed a kitten that age. If he is totally weaned, he should be on a high quality wet food and dry food as a snack, both a kitten type or a food meant for "all-ages" but ideally a kitten food as it is higher in protein and other nutrients.
The general rule for cats of any age is that you should be able to feel their ribs through a layer of fat and muscle but never see them.
Are you worried that your kitten is overweight or underweight?
There is a chart online. http://www.iams.com/en_US/jhtmls/nut...=PN&qi=189#cat
is one, I know there are others but I can't find it right now.
Specifically for kittens, you should check through some of the threads in the pregnant cats & kitten care forum here, as well as this site:www.kitten-rescue.com
, by our own members who have a whole lot of experience with kittens.